Relays are electromechanical switches operated by a flow of electricity in one circuit and controlling the flow of electricity in another circuit. A typical relay consists basically of an electromagnet with a soft iron bar, called an armature, held close to it. A movable contact is connected to the armature in such a way that the contact is held in its normal position by a spring. When the electromagnet is energized, it exerts a force on the armature that overcomes the pull of the spring and moves the contact so as to either complete or break a circuit. When the electromagnet is de-energized, the contact returns to its original position. Variations on this mechanism are possible: some relays have multiple contacts; some are encapsulated; some have built-in circuits that delay contact closure after actuation; some, as in early telephone circuits, advance through a series of positions step by step as they are energized and de-energized, and some relays are of latching type.
Relays are classified by their number of poles and number of throws. The pole of a relay is the terminal common to every path. Each position that the pole can connect to is called a throw. A relay can be made of n poles and m throws. For example, a single-pole-single-throw relay (SPST) has one pole and one throw. A single-pole-double-throw (SPDT) relay has one pole and two throws. A double-pole-double-throw (DPDT) relay has two poles, each with two simultaneously controlled throws.
Relays are then classified into forms. Relay forms are categorized by the number of poles and throws as well as the default position of the relay. Three common relay forms are: A, B, and C. Form A relays are SPST with a default state of normally open. Form B relays are SPST with a default state of normally closed. Form C relays are SPDT and break the connection with one throw before making contact with the other (break-before-make).
Latching relays are the types of relays which can maintain closed and open contact positions without energizing an electromagnet. Short current pulses are used to temporally energize the electromagnet and switch the relay from one contact position to the other. An important advantage of latching relays is that they do not consume power (actually they do not need a power supply) in the quiescent state.
Conventional electromechanical relays have traditionally been fabricated one at a time, by either manual or automated processes. The individual relays produced by such an “assembly-line” type process generally have relatively complicated structures and exhibit high unit-to-unit variability and high unit cost. Conventional electromechanical relays are also relatively large when compared to other electronic components. Size becomes an increasing concern as the packaging density of electronic devices continues to increase.
Many designs and configurations have been used to make latching electromechanical relays. Two forms of conventional latching relays are described in the Engineers' Relay Handbook (Page 3-24, Ref. [1]). A permanent magnet supplies flux to either of two permeable paths that can be completed by an armature. To transfer the armature and its associated contacts from one position to the other requires energizing current through the electromagnetic coil using the correct polarity. One drawback of these traditional latching relay designs is that they require the coil to generate a relatively large reversing magnetic field in order to transfer the armature from one position to the other. This requirement mandates a large number of wire windings for the coil, making the coil size large and impossible or very difficult to fabricate other than using conventional winding methods.
A non-volatile programmable switch is described in U.S. Pat. No. 5,818,316 issued to Shen et al. on Oct. 6, 1998, the entirety of which is incorporated herein by reference. The switch disclosed in this reference includes first and second magnetizable conductors having first and second ends, respectively, each of which is a north or south pole. The ends are mounted for relative movement between a first position in which they are in contact and a second position in which they are insulated from each other. The first conductor is permanently magnetized and the second conductor is switchable in response to a magnetic field applied thereto. Programming means are associated with the second conductor for switchably magnetizing the second conductor so that the second end is alternatively a north or south pole. The first and second ends are held in the first position by magnetic attraction and in the second position by magnetic repulsion.
Another latching relay is described in U.S. Pat. No. 6,469,602 B2 issued to Ruan et al. on Oct. 22, 2002 (claiming priority established by the Provisional Application No. 60/155,757, filed on Sep. 23, 1999), the entirety of which is incorporated herein by reference. The relay disclosed in this reference is operated by providing a movable body sensitive to magnetic fields such that the movable body exhibits a first state corresponding to the open state of the relay and a second state corresponding to the closed state of the relay. A first magnetic field may be provided to induce a magnetic torque in the movable body, and the movable body may be switched between the first state and the second state with a second magnetic field that may be generated by, for example, a conductor formed on a substrate with the relay.
Yet another non-volatile micro relay is described in U.S. Pat. No. 6,124,650 issued to Bishop et al. on Sep. 26, 2000, the entirety of which is incorporated herein by reference. The device disclosed in this reference employs square-loop latchable magnetic material having a magnetization direction capable of being changed in response to exposure to an external magnetic field. The magnetic field is created by a conductor assembly. The attractive or repulsive force between the magnetic poles keeps the switch in the closed or open state.
Each of the prior arts, though providing a unique approach to make latching electromechanical relays and possessing some advantages, has some drawbacks and limitations. Some of them may require large current for switching, and some may require precise relative placement of individual components. These drawbacks and limitations can make manufacturing difficult and costly, and hinder their value in practical applications.
Accordingly, it would be highly desirable to provide an easily switchable electromechanical relay which is also simple and easy to manufacture and use.
It is a purpose of the present invention to provide a new and improved method to make such electromechanical relays.